Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photoreactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. For example, CdTe has an energy bandgap of about 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap semiconductor materials historically used in solar cell applications (e.g., about 1.1 eV for silicon). Also, CdTe converts radiation energy in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in cloudy conditions as compared to other conventional materials. The junction of the n-type layer and the p-type layer is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the cadmium sulfide (CdS) form a p-n heterojunction, where the CdTe layer acts as a p-type layer (i.e., an electron accepting layer) and the CdS layer acts as a n-type layer (i.e., an electron donating layer).
A transparent conductive oxide (“TCO”) layer is commonly used between the window glass and the junction forming layers. This TCO layer provides the front electrical contact on one side of the device and is used to collect and carry the electrical charge produced by the cell. Conversely, a back contact layer is provided on the opposite side of the junction forming layers and is used as the opposite contact of the cell. This back contact layer is adjacent to the p-type layer, such as the cadmium telluride layer in a CdTe PV device.
In forming the PV module, the thin films are typically scribed to form individual cells. For example, the thin film layers can be isolated up to the absorber layer, including the TCO layer, prior to application of the back contact (i.e., commonly referred to as the “P1 scribe”). Additionally, this scribe can then be filled with a nonconductive material, prior to application of a back contact and/or further scribing. In the case of cadmium telluride PV devices, a laser having a relatively high wavelength (e.g., 1064 nanometers) is typically used to form this isolation P1 scribe. However, such a relatively high wavelength laser can be transparent to commonly used TCO layer materials, and consequentially requires a high amount of power to be used. This higher power can lead to jagged scribe line formed in the thin film layers, which can adversely affect the subsequent filling and/or functionalization of the PV cells.
Thus, a need exists for photovoltaic devices having improved isolation scribe and methods of making the same.